HTTP to HTTPS redirect

I would defer to Arie's recommendation. If you have the capability to do so, capture the traffic on the client side and see what the server is sending. You're looking for any object reference, redirect, or otherwise that has http:// in the URL (and that the client subsequently tries to contact). While not obvious, enabling the HTTP-to-HTTPS redirect iRule on the 80 VIP breaks the application in some way, which indicates that something is relying on that 80 VIP.